Suppose Pranali and Prasad started walking from point A, and reached points B and C respectively after 2 hours.
Distance between them = BC = 15√2 km
Since, their speed is same, both travel the same distance in the given time.
∴ AB = AC
Let AB = AC = x km (i)
Now, in ∆ ABC, ∠A = 90°
∴ BC2 = AB2 + AC2 [Pythagoras theorem]
∴ x = \(\sqrt{225}\) [Taking square root of both sides]
∴ x = 15 km
∴ AB = AC = 15km
Now, speed = \(\frac{\text{distance}}{\text{time}}\) = \(\frac{15}{2}\)
= 7.5 km/hr
∴ The speed of Pranali and Prasad is 7.5 km/hour.